Such an apparatus is described in the specification of U.S. Pat. No. 4,944,344 and the corresponding French published patent application No. FR 2 626 053A. Generally, a lock-up clutch includes firstly a coupling element which is adapted to act as a piston and to engage flat against the wall of the casing which faces towards the turbine wheel, when urged into that position by hydraulic pressure which is appropriately controlled for this purpose. The coupling element thus acts as a friction clutch plate locked up against the said wall of the casing. The lock-up clutch also includes an actuating device which is fixed to the coupling element for rotation therewith so as to drive it in rotation. This actuating means is itself adapted to be fixed in rotation to whatever driving element is coupled in rotation to the turbine wheel, usually the hub of the latter.
In the above mentioned United States and French patent specifications, the actuating means comprise a support plate, and the disclosures therein suggest the possibility of driving by a torsion damper comprising two coaxial parts which are mounted for rotation of one with respect to the other against the action of circumferentially acting resilient means.
Having regard to the problems of accommodating the apparatus, and particularly those concerned with its axial size, it is desirable to mount the actuating means of the lock-up clutch at the outer periphery of the turbine wheel, while at the same time ensuring that the resilient members are well guided.